Process for preparing fluoroalkanes



Un fi d S a s Pa en O PROCESS FOR PREPARING FLUOROALKANES F erenc M. Pallos, El Cerrito, and Attila E. Pavlath, Berkeley, Calif., assignors to Stautfer Chemical Company, New York, N.Y., a corporation of Delaware No Drawing. Filed- Jan. 16, 1967, Ser. No. 609,319 5 Claims. (Cl. 260-653) ABSTRACT OF THE DISCLOSURE A process for preparing fiuoroalkanes such as l,l-difiuoroethane and l,l d ifluoropropane by reacting or [SbCl Sb F with trithianes having the formula If on s wherein R, R, and R" are alkyl groups having from 1 to 5 carbon atoms-by heating atatmospheric pressure at a temperature of at least,90 C. and collecting the fiuoroalkanes.

i CH-R terials The exact mechanism for the reaction in the-"process of the present invention is not=fully und erstood. However, it is obvious that one or more'of the carbon-sulfur bonds of the cyclic trithianes is cleaved during the reaction followed by an addition of two fluorine atoms to the ring carbon atom of the certain trithiane and removal of the ring sulfur atoms of. the trithian'eJ'T he fluorochloroarsenic complex and fluorochloroantirnonycomplex act asactive fluorinating agents in the process of this invention.

The preparation of the fluorochloroarsenic complex is described in the chemical literature by L. Kolditz on pages 313-320 of Zeit. Anng. Allg. Chem, 280, 1955. Generally, the preparation of the complex involves the chlorination of arsenic trifluoride with a stoichiometric amount of chlorine. In chlorinating the arsenic trifiuoride, a small amount of water should be added to the arsenic trifiuoride to serve as a catalyst in the reaction. If less than a stoichiometric amount of chlorine is used, then a solution of the complex in arsenic trifluoride can be prepared. The reaction can be run conveniently in conventional glass equipment. The physical properties of the fluorochloroarsenic complex are described in the article by L. Kolditz. The fiuorochloroantimony complex can be prepared in a similar manner by chlorinating antimony trifluoride. The fluorochloroarsenic complex or the fiuorochloroantimony complex can be prepared separately for addition to the trithianes, or they can be prepared in situ for reaction with the trithianes of this invention.

The trithianes that are useful in the practice of this invention are those having the formula R an S 3,367,984 Patented Feb. 6, 1968 ice are alkyl groups having from 1 Preferably, R, R, and R" are all methwherein R, R, and R" to 5 carbon atoms. yl groups.v

A review of the methods of preparing these trithianes is found in an article by E. Champaigne-on pages. '1 through ll of Chem. Rev., vol. 39, 1946. One method described for the preparation of these trithianes involves the reaction of hydrogen sulfide with an aldehyde such as acetaldehyde or propionaldehyde with an acid catalyst to form 2,4,6-trimethyl-1,3,5-trithiane or 2,4,6-triethyl- 1,3,5-trithiane, respectively. Other methods for the preparation of these trithianes are described elsewhere in the literature.

It is preferred to react the certain trithianes of this invention with the fluorochloroarsenic complex or the fluorochloroantimony complex for the preparation of fluoroalkanes by heating them at temperatures above 6 0 C. at atmospheric pressure. A preferred temperature range at atmospheric pressure is about 90 C. to about 160 C. Although the reaction can be run at higher temperatures, there is normally no advantage in doing so.

Also, the reaction can be run at subatmospheric or superatmospheric pressures; however, there is no necessity to do so since the reaction can be conveniently run at atmospheric pressures.

. Although process of this invention .can. be carried out by simply heating a mixture of certaintrithiane of this invention and the fluorochloroarsenic or fluorochloroantimony complex without any mixing and collecting the reactionproduct, it is preferred to agitate the reactants during the reaction. Mechanical mixing has been found useful for the agitation. The mixing of the reactants can best be carried out by forming a slurry of them in an inert liquid such as arsenic trifiuoride, for example.

. The proportion of he fluorochloroarsenic complex or the fluorochloroantimony complex and the certain trithianes is not critical; however, it ispreferred to react at least 6 moles of the complex to 1 mole of the trithiane. When the complex is prepared in situ, the preferred ratio of arsenic trifluoride or antimony trifiuoride to chlorine to the certain trithiane is at least l2:12:1.

The fiuoroalkanes produced by the process of this invention can be recovered by any conventional technique useful for collecting a gaseous product of a solid or liquid phase reaction mixture and then separating the products, if a mixture of products is obtained.

A convenient method for recovering the gaseous products of the process of this invention is to remove any highboiling gaseous material from the product by condensing them, leaving low-boiling products. These can then be condensed by low temperature condensing techniques. Any high-boiling materials can be condensed with tap water in appropriate apparatus, and the low-boiling products such as 1,1-difluoroethane or 1,1-difluoropropane can be condensed with a Dry Ice-acetone mixture in appropriate apparatus. The low-boiling products can be cleaned of any acidic vapors by passing vapors of them through a basic solution such as dilute potassium hydroxide.

In the following examples, several preferred embodiments are described to illustratethe invention. However, it should be understood that the invention is not intended to be limited to the specific examples.

EXAMPLE I The complex [AsCl [AsF was prepared by placing through the glass tubing and bubbled through the liquid r 3 arsenic trifiuoride at room temperature. The chloride addition was continued until a thick slurry of [AsClLQ [AsF in the unreacted portion of liquid arsenic trifluoride was obtained. The iodine crystal catalyzed the reaction between the AsF and C1 A water-packeted distillation condenser was connected to one neck of the reaction fiask. To the condenser'was connected in series an air-cooled trap and another trap cooled with a Dry Ice and acetone mixture. The slurry of [AsCl ]+[AsF was cooled to about 0 C. to 5 C. Thirty grams of 2,4,6-trimethyl-l,3,5-trithiane was added to the slurry with stirring. Next, the reaction flask was heated slowly with an oil bath up to about 160 C., bath temperature. The gaseous reaction products were distilled during the heating. The high-boiling materials were collected in the air-cooled trap, and the low-boiling materials were collected in the trap cooled with the Dry Ice and acetone mixture.

After completion of the reaction as indicated by the cessation of distillation, the trap in the Dry Ice and acetone mixture Was'removed. The material in the trap was vaporized by heating, passed through a dilute solution of KOH, and recondensed in a flask cooled with a Dry Ice and acetone mixture. The clear, recondensed product was found by NMR analysis to be 1,1-difluoroethane.

EXAMPLE II The process of Example I was repeated except that the complex [AsCl +[AsF was replaced with the complex [SbCl ]+[SbF The recondensed product of the reaction was found by analysis to be 1,1-difiuoroethane.

Various modifications of the process of the present invention may be made without departing from the spirit or scope thereof, and it is to be understood that the invention is limited only as defined in the appended claims.

We claim:

1. A process for preparing fluoroalkanes which comprised reacting a complex selected from the group consisting of the fluorochloroarsenic complex, [AsCl +[AsF and the fluorochloroantimony complex, [SbCl +[SbF with a trithiane having the formula wherein R, R, and R" are alkyl groups having from 1 to 5 carbon atomsand recovering said fluoroalkane.

2. The process of claim 1 wherein said complex is the fluorochloroarsenic complex, [AsCl ]+[AsF and said trithiane is 2,4,6-trimethyl-1,3,5-trithiane represented by the formula CH C JI-I err-on,

4. The process of claim 1 wherein said reacting is done by heating at atmospheric pressure at a temperature-of at least 90 C. and wherein the mole ratio of said complex to said trithiane is at least 6:1.

5. The process of claim 2 wherein said reacting is done by heating at atmospheric pressure at a temperature of at least 90 C. and wherein the mole ratio of said complex to said trithiane is at least 6:1.

References Cited UNITED STATES PATENTS 3,321,537 5/1967 Walker et al 260-653 DANIEL D..HORWITZ, Primary Examiner. 

